Re: [PATCH v2 3/3] arm: extend pfn_valid to take into accound freed memory map alignment

On Tue, Jun 29, 2021 at 03:50:23PM +0300, Mike Rapoport wrote:

On Tue, Jun 29, 2021 at 02:52:39PM +0300, Tony Lindgren wrote:

quoted

* Mike Rapoport [off-list ref] [210629 10:51]:

quoted

As it seems, the new version of pfn_valid() decides that last pages are not
valid because of the overflow in memblock_overlaps_region(). As the result,
__sync_icache_dcache() skips flushing these pages.

The patch below should fix this. I've left the prints for now, hopefully
they will not appear anymore. 

Yes this allows the system to boot for me :)

I'm still seeing these three prints though:

...
smp: Brought up 1 node, 2 CPUs
SMP: Total of 2 processors activated (3994.41 BogoMIPS).
CPU: All CPU(s) started in SVC mode.
pfn_valid(__pageblock_pfn_to_page+0x14/0xa8): pfn: afe00: is_map: 0 overlaps: 1
pfn_valid(__pageblock_pfn_to_page+0x28/0xa8): pfn: affff: is_map: 0 overlaps: 1
pfn_valid(__pageblock_pfn_to_page+0x38/0xa8): pfn: afe00: is_map: 0 overlaps: 1

These pfns do have memory map despite they are stolen in
arm_memblock_steal():

memblock_free: [0xaff00000-0xafffffff] arm_memblock_steal+0x50/0x70
memblock_remove: [0xaff00000-0xafffffff] arm_memblock_steal+0x5c/0x70
...
memblock_free: [0xafe00000-0xafefffff] arm_memblock_steal+0x50/0x70
memblock_remove: [0xafe00000-0xafefffff] arm_memblock_steal+0x5c/0x70

But the struct pages there are never initialized.

Actually, with FLATMEM these struct pages will be always set to 0 because
we don't do memory map poisoning with FLATMEM.

I could not find a case where zeroed struct page would cause real trouble,
so I'd say it is more theoretical issue and it can be addressed unrelated
to these changes.

-- 
Sincerely yours,
Mike.

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